It is known that biological cells may be damaged by raising their temperature to approximately 40° C. to 46° C. Hyperthermal treatment, that is, applying temperatures in the range of 40° C. to 46° C. to localized areas of the body has been considered for ablating diseased biological tissue, particularly cancer cells. The application of heat has also been shown to enhance certain biological processes, particularly biological processes associated with healing tissue. Thus low-level heat energy has been applied to areas of damaged tissue in order to encourage biological repair processes.
Microwave energy has been considered for heating biological tissues both for hyperthermal treatment to ablate diseased biological tissues and for other therapeutic purposes such as for enhancing biological processes. U.S. Pat. No. 4,138,998 discusses various uses of microwave energy for therapeutic purposes. A problem with using microwave energy for therapeutic applications is that the microwave energy not only heats the intended target of the treatment, that is, the diseased tissue or the tissue undergoing repair processes, but also adjacent biological tissue. This is particularly a problem in hyperthermal treatments because it can cause excessive damage to healthy tissue in addition to the diseased tissue.